Observations of the Infrared Object, VY Canis Majoris

Infrared colors to 20/2 and optical and infrared spectra have been obtained for the irregular M variable star and bright OH source, VY CMa. Spectra at all wavelengths indicate that it is a supergiant with an effective temperature of 25000_30000 K. Compared with supergiants of the same temperature, VY CMa exhibits a large infrared excess and is one of the brightest objects known at 20 ~1. Its OH emission, near infrared spectra, and far-infrared energy distribution are similar to those of the NML Cyg source; how- ever, it is visually 10 mag brighter. A simple dust-shell model is proposed to explain the observations of VY CMa. Reradiation of energy by the shell is found to be the predominant source of radiation for wavelengths longer than 3 ~ The evolutionary status of VY CMa and NML Cyg is discussed